It has been a recent trend in dynamic random access memory (DRAM) to increase the density of DRAM integrated circuits. However, as higher density DRAM cells are developed, the area available for capacitors that are used in the DRAM cells decreases. In order to decrease the area of capacitors while maintaining reliability standards, it is important to be able to maintain the capacitance of each capacitor while decreasing its area. Recently, capacitors having a three-dimensional structure have been suggested to increase cell capacitance. Such capacitors include, for example, double-stacked, fin-structured, cylindrical, spread-stacked, and box structured capacitors. In addition, where a polysilicon storage node is used, capacitance is increased by forming hemispherical grain polysilicon (HSG) on the polysilicon layer.
Although metal-insulator-metal (MIM) capacitors have the advantages of low interfacial reaction, high capacitance and low contact resistance (R.sub.c), HSG cannot be grown directly on tungsten or other metal conductors in MIM capacitors. Furthermore, the method to manufacture crown or fin structures does not currently apply to MIM capacitors.
The present invention is directed to an improved method for forming a DRAM capacitor. The method forms a capacitor that has a MIM structure and utilizes HSG to create a crown structure.